| 8th of March 2023 |
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| ATNF Colloquium |
| Galactic HII regions, diffuse ionised gas, and structure in the Milky Way |
| Trey Wenger (U. of Wisconsin-Madison) |
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Abstract:
Radio recombination lines (RRLs) are an unobscured tracer of ionized
gas in both the diffuse interstellar medium (ISM) as well as high-mass
star-forming regions. The HII Region Discovery Surveys (HRDS) have
nearly tripled the number of known high-mass star-forming regions in
the Milky Way by detecting RRL emission toward infrared-identified HII
region candidates. HII regions are the classic tracer of structure in
galaxies, and their physical conditions (e.g., metallicity, internal
kinematics) inform models of high-mass star formation and Galactic
chemodynamical evolution. I will give a brief overview of our latest
Australia Telescope Compact Array project, the Southern HII Region
Discovery Survey, and some preliminary results with the first
Galaxy-wide flux-limited HII region sample, including a novel
technique to constrain the Milky Way morphological structure. We
serendipitously discovered (1) a population of HII regions with
ionized gas velocity gradients and (2) RRL emission from diffuse
ionized gas. I will discuss these discoveries, their implications, and
our follow-up work, which will inform both models of high-mass star
formation as well as our understanding of the ISM and Galactic
structure.
As part of a large Australia Telescope Compact Array (ATCA) project, the Southern HII Region Discovery Survey (SHRDS) serendipitously discovered ionized gas velocity gradients in a population of massive star forming regions. The figure above shows one such nebula, the HII region known as G297.651–00.973. The background color is a WISE three-color infrared image (22 micron in red, 12 micron in green, and 3.4 micron in blue), the black contours represent the SHRDS radio continuum brightness, and the colored contours represent the ionized gas velocity field. What is the origin and nature of these ionized gas velocity gradients? Follow-up work with the ATCA and the Very Large Array will hopefully answer these questions. |